There are numerous potential applications of carbon nanotubes (CNTs) because of their unique mechanical, physical, electrical, chemical, and biological properties. For example, ultra low resistance conductors, semiconductors, highly efficient electron emitters, ultra-strong lightweight fibers for structural applications, lasers, and gas sensors can all be manufactured by using CNTs.
A variety of synthesis techniques for preparing CNTs exist. These techniques include for example carbon arc, laser ablation, chemical vapor deposition, high pressure carbon monoxide process (HiPco), cobalt-molybdenum catalyst process (CoMoCat). Depending on the preparation method, CNTs may be metallic and semiconducting.
The incorporation of non-carbon materials into CNTs may lead to even more diverse range of applications, for example, in improved gaseous storage media or electronic devices. In a publication entitled “Titanium-Decorated Carbon Nanotubes as a Potential High-Capacity Hydrogen Storage Medium”, Physical Review Letters, 2005, Vol. 94, pages 175501-1 to 175501-4, Yildirim et al. describe that each titanium atom adsorbed on a single-wall CNT (SWCNT) may theoretically bind up to four hydrogen molecules.
In a publication entitled “Titanium Monomers and Wires Adsorbed on Carbon Nanotubes: A First Principles Study”, Nanotechnology, 2006, Vol. 17, pages 1154-1159, Fagan et al. describe a theoretical study of Ti monomers and wires interacting with a semiconductor single-wall carbon nanotube, by inside as well as outside faces. Fagan et al. only provide a theoretical study without actual data.
Electrochemical supercapacitors based on high surface area carbon have been demonstrated since the late fifties. However, only in the nineties did supercapacitors become important, particularly for the development of fuel cell and hybrid electric vehicles. This is because a capacitor can discharge and recharge far faster than a battery, making it ideal both for generating bursts of speed and for soaking up the energy collected by regenerative braking of the vehicle. Capacitors may thus be able to bridge the gap that exists between speed and endurance.
Therefore, there exists a need for new or improved capacitors for providing high capacitance.